Cathode sleeve



July 13, 1943.

N R. SMITH CATHODE SLEEVE Filed Jan. 1, 1942 INVENTOR Newe R. Smifh.

B @mzmww ATTEIR NEY Patented July 13, 1943 CATHODE SLEEVE Newell R. Smith, Bloomfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 1, 1942, Serial No. 425,289

Claims.

My invention relates to cathodes, particularly to indirectly heated cathode sleeves for electron discharge devices and the like.

Cathode sleeves exteriorly coated with electron emissive compounds and internally receiving an insulated heating element have heretofore been made by either drawing seamless tubing to the desired length and diameter or by wrapping flat sheet metal stock around a mandrel and closing the seam along the side of the sleeve by welding or by interlocking the edges of the sheet. The drawn tubing is expensive because of the difficulty and slowness of the drawing operation. The seamed cathode sleeve is impractical, particularly in the small sizes because tools are difiicult to maintain which can fold and interlock the edges of the sheet metal and except for small embossed beads, only straight sided cylindrical sleeves can be made in factory production.

An object of my invention is a cathode sleeve that is easy and inexpensive to make and that does not require fragile and expensive tools.

A further and more specific object of my invention is a cathode sleeve of uniform wall thickness even along the seam of the sleeve.

A still further object of my invention is a cathode sleeve which, by factory production methods, may be made with any desired external surface configuration.

The cathode according to my invention comprises a tubular metal sleeve fabricated from fiat sheet metal stock with a butt seam longitudinally along the side of the sleeve. The sleeve is made by rolling the sheet metal flat stock into a cylinder larger in diameter than the finished sleeve. By swaging or hammering the external surface of the wrapped cylinder with a series of rapidly dealt blows from a heavy die, the sleeve may be reduced to the desired external size and configuration. Stop beads, circumferential grooves and tapers may be conveniently formed in the external surface of the swaged sleeve. Irregular shapes may be made which cannot be formed in sleeves made in the conventional method of making lock seamed cathode sleeves. The sleeve is preferably of a refractory metal, such as nickel, which forms a good basis for the electron emissive compounds.

The characteristic features of my invention are defined in the appended claims and preferred embodiments thereof are described in the following specification and shown in the accompanying drawing in which Figure 1 shows in section an electron discharge device embodying my novel cathode sleeve, Figure 2 is an end detailed view of the cathode sleeve of Figure 1, Figures 3, 4, 5, 6, 7 and 8 show cathode sleeves embodying my invention with respective and desirable external shapes, and Figure 9 shows one apparatus for making my improved cathode sleeve.

For convenience of illustration my novel cathode sleeve is shown in a conventional radio tube although the cathode may of course be used in any electron discharge device, lamp or the like. The conventional radio receiving tube shown in Figure 1 comprises an envelope 1 containing an electrode assembly including an anode 2, a grid 3, if desired, and a cathode 4, the electrodes being supported at their ends in insulating spacers 5. The cathode is externally coated along its center section with an electron emissive compound, such as barium-strontium oxides, and the end sections of the sleeve are snugly fitted into the insulating spacers. An insulated heating coil is inserted at the lower end of the sleeve for heating the cathode coating to emission temperature.

My novel cathode sleeve comprises a one-piece wrapped tube with the butt seam 6 along one side and with an integral stop boss or bead l for hearing against one of the insulating spacers. The other end of the sleeve may easily be tapered, if desired, to facilitate its insertion in its spacer hole.

In manufacturing my novel sleeve, according to one characteristic feature of my invention, a wrapped butt seamed tube is swaged to reduce the diameter of the tube and to obtain the desired external configuration. The fiat stock may be uni-eeled and fed through a conventional curling die 20, Figure 9, which rolls the stock into substantially round tubing. The tubing is fed forward step-by-step through the progressive split dies 2i, each step being equal to the desired length of the finished sleeve. The recesses 22 in the successive stations in the dies progressively reduce in size and gradually approach the desired external shape of the finished sleeve. The upper dies reciprocate rapidly, hammering the tubing as the tubing is turned or rolled slowly back andforth in the lower die. The curling die may conveniently be oscillated for rotating the tubing. The joined ends of the finished sleeves may be broken off, or if desired cut off as with a knife 23. It has been found that rapidly delivered hammer blows on the outer surface of the tube as it is rotated between the hammers reduce the diameter of the tube without materially distorting the tube and as the metal is Worked the diameter is reduced, the metal in the outer layers or outer surface region of the tube is permanently hardened, apparently placing the metal fibers in the outer surface of the cylinder under compression and forcing the butted edges of the wrapped tube into firm pressure contact. Any force from the inside of the swaged and workor strain-hardened cylinder tending to separate the butted edges of the seam must overcome the permanent strains in the metal. A cathode may thus be formed with a closed butt seam which will not spring open as in the case of the conventionally wrapped cylinder without swaging. Where the cathode may be roughly handled or subjected to severe mechanical stress, it may be desirable to tin the edges of the cathode stock with a high melting solder, such as silver, or silver alloy, or other alloy, and heat the sleeve, before or after swaging, to solder and join the edges. The closed butt seam along the sides of the cylinder thus provides a cathode sleeve of uniform wall thickness and is to be distinguished from the conventional cathode sleeve having a locked seam with four thicknesses, or a welded seam with two or three of the sheet metal stock along the seam.

In addition to providing a sleeve of uniform wall thickness circumferentially of the sleeve, the sleeve is easily shaped to any desired external configuration. One or both ends of the sleeve may be tapered as shown at 8 in Figures 3, 6, 7 or 8, or the coated area of the sleeve may be tapered or provided with steps of varying diameter as shown in Figure 4 or 6. By forming the insulating spacer holes slightly undersize, the tapered ends of the sleeve are easily pressed and wedged in place to insure against loose cathodeto-spacer contact and troublesome microphonic noises in the tube. An enlarged portion 9, Figure 6, of the barrel may place a portion of the coated area of the sleeve nearer to a concentric grid than is possible with the conventional straight sided sleeve. That is, for a given cathode and grid diameter, the distance between the cathode sleeve and the grid side rods may be increased by reducing the diameter of the end sections of the sleeve. A further and particularlyuseful application of my novel cathode sleeve shown in Figure 4 comprises two end-to-end emitting sections on one sleeve, the emitting sections being of two diameters joined by a gradually tapered shoulder in the upper insulating spacer. This sleeve is particularly useful in the so-called duplex diodetriode radio tubes in which a separate electrode assembly is mounted opposite each emitting section of the cathode. The reduced upper section 4a of the sleeve permits the top spacer to be lowered into place without scraping the emitting coating. Alternatively a tapered bead as shown in Figure 5 may be provided on the sleeve and, in combination with a top spacer with an oversized hole, may be assembled without disturbing the emitting coating on the upper section.

A plurality of concentric grooves may be easily swaged in the sleeve as shown in Figure 8. When these grooves are coated with emitting material and mounted opposite spaces between the convolutions in a grid, a so-called beam forming tube may be easily made. On the end of this sleeve as well as on any of the sleeves shown, an integral tab it) may be swaged for electrical connection and support.

Since the cathode sleeve according to my invention is made with a butt seam and is externally swaged, its shape, size and configuration may be varied at will. This advantage becomes apparent when compared with the conventional sleeve that must be rolled from flat stock and must be formed with straight cylindrical sides from end-to-end. In addition to affording desired irregular shapes for the emitting surface, the sleeve does not have the disadvantage of a bulky asymmetrical seam along its side. Cathode sleeves according to my invention are inexpensive and easy to make.

I claim:

1. A cathode comprising a sheet metal member wrapped to form a cylinder having a butt seam along its side, the cylinder being externally swaged on its outer surface to place permanent strains in the outer surface region of its wall tending to bring the edges of the sheet along the seam together and to close the sleeve, and an electron emission coating on the exterior surface of the cylinder.

2. A cathode comprising a tubular metal sleeve fabricated from flat sheet metal stock wrapped to form a sleeve with a butt seam along its side, and with substantially uniform Wall thickness throughout the circumference of the sleeve, the outer surface of the tube being permanently hardened by hammering to close the edges of the sleeve along the seam, and electron emissive compounds coated on the external surface of said sleeve.

3. A cathode comprising a wrapped tubular metal sleeve with a butt seam along its side, the Walls of the tube being worked by hammering to close the edges of the member along the seam, the external surface of the sleeve between its ends being swaged to at least two different diameters over adjacent end-to-end sections, said sections being coated with an electron emissive compound, and one end of the sleeve being swaged to a slight taper.

4. An electron discharge device comprising spaced insulating spacers, an anode and a cathode between said spacers and supported at their ends by said spacers, holes in each spacer to receive the ends of the cathode, the cathode comprising a tubular sleeve with a closed butt seam along one side, the center section of the sleeve being coated with an electron emissive compound and being swaged to an irregular configuration, and at least one end of the sleeve being swaged and tapered to fit snugly in its spacer hole.

5. A tubular butt seamed cathode sleeve, the external surface of the sleeve, intermediate the end portions of the sleeve, being electron emissive, the intermediate emissive portion of the sleeve being of a circumferential size larger than the end portions of the sleeve, the butt seam being closed throughout the length of said sleeve.

NEWELL E. SMITH. 

